This invention relates to a process for cleansing animal tissue and removal and or inactivation of pathogens in animal tissue such as human tissue including bone or any tissue, and more particularly, to cleansing the tissue for use as an implant.
It is desirable to physically clean a donor tissue of contaminants such as blood and to remove or inactivate potential pathogens (viruses, bacteria, fungi, mycoplasma and prions) for clinical use of the tissue such as bone as a grafting agent, or connective tissue that will be used to repair tendons or other connective tissue. The best way to accomplish this is to physically remove contaminants and pathogens as much as possible, then attack any remaining pathogens particles such as viruses and bacteria in the bone or connective tissue with one or more inactivating solutions.
During life, bone and connective tissue, whether it is allogenic, autogenic, or xenografic, is normally sterile with respect to bacteria. This is because the immune system keeps the body aseptic. Any significant build up of bacteria internally is abnormal and can quickly lead to death (sepsis). However, in the case of death, even from causes other than sepsis, bacteria can enter bone or connective tissue once life has ceased. The usual routes are migration from the digestive system or from degradation processes due to storage and handling. Therefore, bacteria that is present in recovered tissue tends to be more on the surface or in areas easily accessible from the surface.
Viruses, however, are more deeply imbedded. Unlike bacteria, viruses can be present throughout the body during life without causing fatal disease or even obvious sickness. Viruses enter tissue such as bone and connective tissue through the blood supply and can be present in capillaries deep within the internal cavities of the tissue, especially Haversian systems of bone.
The disinfecting processes normally employed to clean and disinfect bone and connective tissue prior to transplant are mainly topical, and do not penetrate deeply into bone or other tissues. As such, they are effective as topical disinfectants, but do not address potential internal viral contamination well. Sterilization is one option, but sterilization techniques typically damage bone and tissue when employed in the dose required to inactivate viruses.
A centrifuge may be employed as part of a bone cleaning system where the centrifugal forces and increased gravity force materials and substances from the bone in both a dry stage and a wet stage to remove bone marrow and cellular debris. This centrifuge action may provide effective cleaning/disinfecting for some contaminants and pathogens, but the present inventors believe that it does not treat viruses, especially those in the internal tissue cavities, effectively.
U.S. Pat. Nos. 6,682,695, 6,635,222 and 6,346,216 as well as published U.S. patent applications Ser. Nos. 20040013562, 20040013561, 20030213920, 20030186421, 20030185702, 20030180181, 20030162163, 20030161753, 20030124023, 20030095890, 20030064000, 20030059920, 20030059338, 20030049245, 20030031584, 20030031581, 20030012687, 20020155519 all disclose methods for sterilizing biological materials in which radiation protectants may be added to the material prior to the sterilization process. These protectants are so designed to as to reduce or prevent damage to the tissue during the radiation sterilization treatment. The present invention is a faster, more effective, thorough and efficient approach of introducing radiation protectants, cryoprotectants, mechanically useful substances, biologically useful substances or biologically active agents into the biological material such as tissue prior to or during the sterilization process compared to the previous methods.
The present inventors recognize that a much better approach is to use a cleansing and pathogen inactivation process that reaches all the internal spaces of the tissue and which removes or inactivates viruses. Internal bone spaces can be reached by a pressure/flow process employing pumps as disclosed in commonly owned U.S. Pat. No. 5,846,484, or a vacuum process as disclosed in commonly owned U.S. Pat. No. 5,513,662. Of interest also is published International application no. WO 00/29037
However, the patented processes are cumbersome to implement and use potentially unreliable liquid seals in a pressurized vessel. These patented systems are not desirable for these reasons.